1. Field of the Invention
The present invention relates generally to a radio network, a relay node, a core node, a relay transmission method used in the same and a program thereof. More particularly, the invention relates to a relay route setting method and a relay transmission method in a cellular system, in which a plurality of nodes are connected by a radio network.
2. Description of the Related Art
A cell structure in the conventional cellular system is illustrated in FIG. 20. In FIG. 20, the reference numeral 401 denotes a cell and 402 denotes a base station (node). As shown in FIG. 20, a service area is constructed by arranging a plurality of cells.
Each node is connected to a wired backbone network 404 through wire lines 403 for transmitting service signals, such as voice, data and so forth and various control signals. It should be noted that the node and the wired backbone network may be connected by hierarchically providing line concentration stations there-between.
A terminal station 405 communicates with a node 402 for performing transmission and reception of various signals to be transmitted by a wired backbone network 404 through wire lines 403. In the wired backbone network, not only the radio base station (node), but also server equipment provide a management of position information of the terminal station 405, a billing process and so forth.
In order to increase numbers of subscribers of a cellular system, such as a cellular telephone system, a subscriber fixed wireless access and so forth, the radius of each cell is reduced, thus reducing the process load in each node. When the system is constructed with such micro cells, quite a large number of nodes are arranged in order to reliably establish the service area.
On the other hand, when a high density data transmission method of multi-value modulation or the like is applied for adapting to a high speed data transmission, the service area to be covered by one node inherently becomes narrow for providing reliable quality. Even in such a case, quite a large number of nodes have to be arranged for reliably establishing the service area.
Furthermore, although the conventional cellular system has been mainly designed in a quasi-microwave band and microwave band, due to tightness of frequencies, it is desirable to establish the cellular system using submillimeter wave or millimeter wave. When frequency becomes higher, diffraction effect of the radio wave is reduced to make straightening characteristics significant, and it causes difficulty in non line-of-sight communication to inherently narrow the area of service in each node. Namely, even in such a case, the service area has to be established with micro cells to install quite a large number of nodes.
When a system is established with a large number of micro cells, it becomes essential to establish a wired network for connecting the node group to the backbone network. However, in order for a connection between a large number of geographically concentrated nodes and the backbone network, wire line networks have to be extended to every place, thus inherently increasing the cost of the overall system. Therefore, there is a method to establish the connection between nodes with wireless communication for relay transmission to expand the service area.
Setting of the relaying method dominates a capacity because capacity of the cellular system is restricted by interference, and tolerance of interference depends upon the setting of the relaying. In a route method that decreases the number of relay nodes, the so-called “minimum hop routing” method, throughput or system capacity cannot be always at maximum relaying route for lacking of reception power due to the distance between relay nodes and obstacles.
For achieving improvement of throughput and large circuit capacity of the overall system, a method of setting the relay route becomes important. However, heretofore, there is no relay route setting method specialized for a radio relay transmission type cellular system in a configuration where a core node is arranged with a large number of micro cells and is connected to the wired backbone network thereby solving a problem of interference between the cells which causes problem in the cellular system.